1. Field of the Invention
The present invention relates to an image forming apparatus in which an electrostatic image is formed by emitting a light, such as a laser beam to a charged image bearing member, and the electrostatic image is developed to print the image, particularly to an image forming apparatus which is capable of automatically adjusting starting points of the printing in accordance with the image forming ranges.
2. Description of the Prior Art
A known type of image forming apparatus for plural color printing includes a drum shaped sensitive member 100 as an image bearing member, as shown in FIG. 1. Around the sensitive member 100, there is disposed a first charger 101, a first exposing portion 102, a first developing unit 103, a second charger 104, a second exposing portion 105, a second developing unit 106, a stripping charger 107, a cleaner 110, and discharger 109 in a rotational direction of the sensitive member 100 in that order. The sensitive member 100 is uniformly charged by the first charger 101, a first electrostatic image is formed at the first exposing portion 102, and the image is developed by the first developing unit 103 such that the image is visible at a first color. After that, the sensitive member 100 is charger by the second charger 104, a second electrostatic image is formed at the second exposing portion 105, and the image is developed by the second developing unit 106 to being visible the image at a second color. Two kind toners for the two color is treated to equalize the polarity of one toner to a polarity of another, the two color image is transferred on a member to be transferred, and after the transferring, a residual toner on the sensitive member 100 is cleaned by the cleaner 110 and the electrostatic image is eliminated by the discharger 109. An image forming process is accomplished by carrying out the above pressure.
In that image forming apparatus, it is very important thing to eliminate a gap between a print starting point of the first color and a print starting point of the second color for obtaining a clear color print image. However, in a conventional image forming apparatus, an adjustment of the two print starting points is carried out by an operator an all such occasions. It is very difficult and troublesome thing for the operator to carry out the adjustment in ivery time.